(1) Field of the Invention
The present invention relates to a pellicle film having a reflection-preventive layer, which is used as a pellicle as a dust-proof cover for a photomask or reticule, and a process for the preparation thereof. More particularly, the present invention relates to a pellicle film having a reflection-preventive layer of a specific polyfluoro(meth)acrylate formed on one or both of the surfaces of a transparent film of a cellulose derivative, and a process for the preparation thereof.
(2) Description of the Prior Art
There has been proposed a method in which a dust-proof cover called "pellicle" is used in combination with a photomask or reticule at the step on the light-exposing a semiconductor to prevent influences of dust on the light-exposing step and improve the productivity (see Japanese Patent Publication No. 54-28716). The pellicle has a structure comprising a pellicle film set on one side face of a pellicle frame, and the pellicle is used in the state overlapped on a photomask or reticule.
A single-layer film of nitrocellulose has been mainly used as the pellicle film of this pellicle, and for improving the throughput at the light-exposing step, there have been proposed pellicle films having a reflection-preventive layer formed on a transparent film of nitrocellulose (see Japanese Patent Application Laid-Open Specification No. 60-237450, No. 61-53601 or No. 61-209449).
More specifically, Japanese Patent Application Laid-Open Specification No. 60-237450 teaches that a fluorine type polymer or silicon type polymer is used for the reflection-preventive layer, and as the fluorine type polymer, there are disclosed a tetrafluoroethylene/vinylidene fluoride copolymer and a tetrafluoroethylene/vinylidene fluoride/hexafluoropropylene copolymer. Furthermore, Japanese Patent Application Laid-Open Specification No. 61-53601 teaches that a fluorine type polymer or a silicon type polymer is used for the reflection-preventive layer, and a tetrafluoroethylene/vinylidene fluoride/hexafluoropropylene copolymer is specifically disclosed as the fluorine type polymer. Japanese Patent Application Laid-Open Specification No. 61-209449 teaches that a fluorine type polymer including a polyfluoro(meth)acrylate can be used for the reflection-preventive layer, and a tetrafluoroethylene/vinylidene fluoride/hexafluoropropylene copolymer is specifically disclosed as in the foregoing references.
These conventional pellicle films having a reflection-preventive layer are prepared according to the process in which solutions for the transparent film and the reflection-preventive layer are supplied onto a substrate and the rotational film-forming method is adopted. This process, however, is defective in that the light transmission is low and the bonding force between the transparent film and the reflection-preventive layer is weak. Accordingly, when the pellicle film formed on the substrate is peeled from the substrate, it is necessary to swell the pellicle film in water, and there is a risk of formation of wrinkles when the peeled pellicle film is dried. Moreover, the productivity is low.